Positron emission mammography (PEM) is a form of positron emission tomography (PET) that uses high-resolution, mini-camera detection technology for imaging the breast. As with PET, PEM provides functional rather than anatomic information about the breast. PEM has been studied primarily for use in presurgical planning and evaluation of breast lesions.

Positron emission mammography (PEM) is a form of positron emission tomography (PET) that uses a high-resolution, mini-camera detection technology for imaging the breast. As with PET, a radiotracer, usually fluorodeoxyglucose fluorine 18 (FDG) is administered, and the camera is used to provide a higher resolution image of a limited section of the body than would be achievable with FDG-PET. Gentle compression is used, and the detector(s) are mounted directly on the compression paddle(s). PEM was developed to overcome the limitations of PET for detecting breast cancer tumors. Patients usually are supine for PET procedures, and breast tissue may spread over the chest wall, making it potentially difficult to differentiate breast lesions from other organs that take up the radiotracer. PET’s resolution is generally limited to approximately 5 mm, which may not detect early breast cancer tumors. PEM allows for the detection of lesions as small as 2 to 3 mm and creates images that are more easily comparedwith mammography, because they are acquired in the same position. Three-dimensional reconstruction of PEM images is also possible. As with PET, PEM provides functional rather than anatomic information about the breast. In PEM studies, exclusion criteria included some patients with diabetes.

Radiation Dose Associated With PEM

The label-recommended dose of FDG for PEM is 370 MBq (10 mCi). Hendrick (2010) calculated mean glandular doses, and from those, lifetime attributable risk (LAR) of cancer for film mammography, digital mammography, breast-specific gamma imaging (BSGI), and PEM. The author, who has been a consultant to GE Healthcare and a member of the medical advisory boards of Koning (which is working on dedicated breast computed tomography) and Bracco (magnetic resonance [MR] contrast agents), used BEIR VII Group risk estimates to gauge the risks of radiation-induced cancer incidence and mortality from breast imaging studies. Estimated LAR of cancer for a patient with average-sized compressed breast during mammography of 5.3 cm (risks would be higher for larger breasts) for a single breast procedure at age 40 years is:

5 per 100,000 for digital mammography (breast cancer only);

7 per 100,000 for screen film mammography (breast cancer only);

55 to 82 per 100,000 for BSGI (depending on the dose of technetium Tc 99m sestamibi); and

75 per 100,000 for PEM.

The corresponding LAR of cancer mortality at age 40 years is:

1.3 per 100,000 for digital mammography (breast cancer only);

1.7 per 100,000 for screen film mammography (breast cancer only);

26 to 39 per 100,000 for BSGI; and

31 per 100,000 for PEM.

A major difference in the impact of radiation between mammography, on the one hand, and BSGI or PEM, on the other, is that for mammography, radiation dose is limited to the breast, whereas with BSGI and PEM, all organs are irradiated. Furthermore, as one ages, risk of cancer induction from radiation exposure decreases more rapidly for the breast than for other radiosensitive organs. Organs at highest risk for cancer are the bladder with PEM and the colon with BSGI; these cancers, along with lung cancer, are also less curable than breast cancer. Thus, the distribution of radiation throughout the body adds to the risks associated with BSGI and PEM. Hendrick concluded that:

“results reported herein indicate that BSGI and PEM are not good candidate procedures for breast cancer screening because of the associated higher risks for cancer induction per study compared with the risks associated with existing modalities such as mammography, breast US [ultrasound], and breast MR imaging. The benefit-to-risk ratio for BSGI and PEM may be different in women known to have breast cancer, in whom additional information about the extent of disease may better guide treatment.”

O’Connor and colleagues (2010) estimated the LAR of cancer and cancer mortality from use of digital mammography, screen film mammography, PEM, and molecular breast imaging (MBI). Only results for digital mammography and PEM are reported here. The study concluded that, in a group of 100,000 women at age 80 years, a single digital mammogram at age 40 years would induce 4.7 cancers with 1.0 cancer deaths; 2.2 cancers with 0.5 cancer deaths for a mammogram at age 50; 0.9 cancers with 0.2 cancer deaths for a mammogram at age 60; and 0.2 cancers with 0.0 cancer deaths for a mammogram at age 70. Comparable numbers for PEM would be 36 cancers and 17 cancer deaths for PEM at age 40; 30 cancers and 15 cancer deaths for PEM at age 50; 22 cancers and 12 cancer deaths for PEM at age 60; and 9.5 cancers and 5.2 cancer deaths for PEM at age 70. The authors also analyzed the cumulative effect of annual screening between ages 40 and 80, as well as between ages 50 and 80. For women at age 80 who were screened annually from ages 40 to 80, digital mammography would induce 56 cancers with 15 cancer deaths; for PEM, the analogous numbers were 800 cancers and 408 cancer deaths. For women at age 80 who were screened annually from ages 50 to 80, digital mammography would induce 21 cancers with 6 cancer deaths; for PEM, the analogous numbers were 442 cancers and 248 cancer deaths. However, background radiation from age 0 to 80 is estimated to induce 2174 cancers and 1011 cancer deaths. These calculations, like all estimated health effects of radiation exposure, are based on several assumptions. Comparing digital mammography and PEM, two conclusions are clear: Many more cancers are induced by PEM than by digital mammography; and for both modalities, adding annual screening from 40 to 49 roughly doubles the number of induced cancers. In a benefit-risk calculation performed for digital mammography but not for PEM, O’Connor and colleagues nevertheless reported that the benefit-risk ratio of annual screening is still approximately 3 to 1 for women in their 40s, although it is much higher for women 50 and older. Like Hendrick, the authors concluded that “if molecular imaging techniques [including PEM] are to be of value in screening for breast cancer, then the administered doses need to be substantially reduced to better match the effective doses of mammography.”

The American College of Radiology (ACR) has assigned a relative radiation level (effective dose) of 10 to 30 mSv to PEM. ACR has also stated that, because of radiation dose, PEM and BSGI in their present form are not indicated for screening.

Because the use of BSGI and MBI have been proposed for women at high risk of breast cancer, it should be mentioned that there is controversy and speculation whether some women (eg, those with BRCA mutations) have heightened radiosensitivity. If women with BRCA mutations are more radiosensitive than the general population, the previous estimates may underestimate the risks they face from breast imaging with ionizing radiation (ie, mammography, BSGI, MBI, PEM, single-photon emission computed tomography, breast-specific computed tomography, and tomosynthesis; ultrasound and magnetic resonance imaging do not use radiation). More research will be needed to resolve this issue. Also, risks associated with radiation exposure will be greater for women at high risk of breast cancer, whether or not they are more radiosensitive, because they start screening at a younger age, when the risks associated with radiation exposure are increased.

In August 2003, the PEM 2400 PET Scanner (PEM Technologies, Inc., Ridgefield, NJ) was cleared for marketing by the U.S. Food and Drug Administration (FDA) through the 510(k) process. The FDA determined that this device was substantially equivalent to existing devices for “medical purposes to image and measure the distribution of injected positron emitting radiopharmaceuticals in human beings for the purpose of determining various metabolic and physiologic functions within the human body.”

In March 2009, the Naviscan PEM Flex™ Solo II™ High Resolution PET Scanner (Naviscan, San Diego, CA) was cleared for marketing by the FDA through the 510(k) process for the same indication. The PEM 2400 PET Scanner was the predicate device. The newer device has been described by the manufacturer as “a high spatial resolution, small field-of-view PET imaging system specifically developed for close-range, spot, i.e., limited field, imaging.”

In December 2013, Naviscan was acquired by Compañía Mexicana de Radiología SA (Queretaro, Mexico), which currently markets the Naviscan Solo II™ Breast PET Scanner in the United States (CMR Naviscan, Carlsbad, CA).

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